1. Field of the Invention
The present invention relates to a video data editing apparatus that uses an optical disc as an editing medium for video data, a computer-readable recording medium that stores an editing program, an optical disc for use as a recording medium of a video data editing apparatus, and a reproduction apparatus for an optical disc.
2. Description of the Background Art
Video editors in the film and broadcasting industries make full use of their skill and experience when editing the great variety of video productions that reach the market. While movie fans and home video makers may not possess such skill or experience, many are still inspired by professional editing to try video editing for themselves. This creates a demand for a domestic video editing apparatus that can perform advanced video editing while still being easy to use.
While video editing generally involves a variety of operations, domestic video editing apparatuses that are likely to appear on the market in the near future will especially require an advanced scene linking function. Such function links a number of scenes to form a single work.
When linking scenes using conventional domestic equipment, the user connects two video cassette recorders to form a dubbing system. The operations performed when linking scenes using this kind of dubbing system are described below.
FIG. 1A shows a video editing setup using video cassette recorders that are respectively capable of recording and playing back video signals. The setup of FIG. 1A includes the video cassette 301 that records the source video, the video cassette 302 for recording the editing result, and two video cassette recorders 303 and 304 for playing back and recording video images on the video cassettes 301 and 302. In this example, the user attempts to perform the editing operation shown in FIG. 1B using the setup of FIG. 1A.
FIG. 1B show the relationship between the source materials to be edited and the editing result. In this example, the user plays back scene 505 that is located between time t5 and time t10 of the source materials, scene 506 that is located between time t13 and t21, and scene 507 that is located between time t23 and t25 and attempts to produce and editing result that is only composed of these scenes.
With the setup of FIG. 1A, the user sets the video cassette 301 including the source materials into the video cassette recorder 303 and the video cassette 302 for recording the editing result into the video cassette recorder 304.
After setting the video cassettes 301 and 302, the user presses the fast-forward button on the operation panel of the video cassette recorder 303 (as shown by 1 in FIG. 1A) to search for the start of scene 505. Next, the user presses the play button on the operation panel of the video cassette recorder 303 (as shown by 2 in FIG. 1A) to reproduce scene 505. At the same time, the user presses the record button on the operation panel of the video cassette recorder 304 (as shown by 3 in FIG. 1A) to commence recording. When scene 505 has finished, the user stops the operation of both video cassette recorders 303 and 304. The user then fast-forwards the video cassette to the start of scene 506, and then simultaneously commences the playback by video cassette recorder 303 and the recording by video cassette recorder 304. After completing the above process for scenes 506 and 507, the user has the video cassette recorders 303 and 304 respectively rewind the video cassettes 301 and 302 to complete the editing operation.
If the scene linking operation described above could be performed with ease at the home, users would then be able to easily manage programs that have been recorded on a large number of magnetic tape cassettes.
A first problem with the video editing setup described above though is that the source material and editing result need to be recorded on separate recording media, meaning that two video cassette recorders need to be used for playing back and recording the respective recording media. This greatly increases the scale of the video editing setup.
A second problem is that the need to reproduce the video images between time t5.about.t10, t13.about.t21, and time t23.about.t25 using video cassette recorder 303 makes the video editing very time consuming. Here, the longer the video excerpts that compose the editing result, the longer the reproduction time and the editing time, meaning that the editing of long source materials can take an extremely long time.
To complete the above linking process in a short time with small-scale equipment, it would be ideal for the pieces of the recording media that record the desired video images to be simply linked together, as with the conventional splicing of sections of magnetic tape. When the source materials are stored as analog video signals, there may be no significant problems should the sections of magnetic tape storing the desired materials be spliced together. However, when linking system streams that have been highly compressed according to MPEG techniques, there are the problems that the video reproduction can be interrupted or disturbed at the joins between the spliced sections. Here, the expression "system stream" refers to video data and audio data that are multiplexed together, with such streams also being called "audio-visual data (AV data)" in this specification.
One of the causes of the above problem is the assigning of variable-length code to video frames in a video stream. When encoding a video stream, an optimal amount of code is assigned to each display cycle in order to strike a good balance between to the complexity of the image to be displayed and the amount of data that is already stored in the buffer of the video decoder.
Since precise calculations are performed when assigning code within a video stream, it can be ensured that no underflows or overflows will occur in the decoder buffer when a single video stream is reproduced in its original form. However, when separately encoded former and latter video streams are linked together, the latter video stream will be inputted into the buffer of a video decoder with no consideration to the amount of data already accumulated in the video decoder buffer at the end of reproduction of the former video stream. When this happens, there is a clear possibility of an overflow or an underflow occurring in the video decoder buffer. When linking partial sections of a system stream in the same way as in FIG. 1B, there is the possibility of an overflow or an underflow occurring in the video decoder buffer when the reproduction proceeds from a former section to a latter section.
Reproduction of video without interruptions and disturbances is called seamless reproduction. To perform seamless reproduction of linked sections, it is necessary to temporarily convert the former section and latter section into video signals and audio signals and to then re-encode these signals to convert the signals of the former section and latter section into a single video stream and audio stream. The time taken by such re-encoding is proportional to the amount of data in the video streams and audio streams of the edited source materials. As a result, when the source materials contain a large amount of data, this process will be very time-consuming.
To perform AV synchronization during the reproduction of an MPEG system stream, the time stamps that show the respective reproduction times of a video stream and an audio stream must be consecutive. Conventionally, MPEG standards have focused on the consecutive reproduction of one stream from start to end, so that seamless reproduction has not been possible for two MPEG streams which do not have consecutive time stamps. As a result, during editing, it has been necessary to give at least one of the linked MPEG streams time stamps that are continuous with the time stamps in the other MPEG stream, meaning that the latter MPEG stream has had to be re-encoded in its entirety.